Apr., 1921] 
HANSON — MALVACEAE IN TEXAS 
199 
H. coulteri occurred frequently on rocky hillsides and cliffs along the Rio 
Grande. Malva parviflora was a common weed in waste places in towns. 
Pavonia lasiopetala was found in only one place, in a dry, rocky ravine near 
New Braunfels. Sida diffusa and S. filiformis occurred commonly in 
sandy and rocky places, in chaparral, and on the open plains from the 
Rio Grande to Pecos. S. hastata was frequent in woods, open plains, in 
rocky places, and as a weed in waste places throughout the region. Sphaeral- 
cea cuspidata was frequent in sandy to clay soil in valleys and on low plains 
and as a weed in fields from the Rio Grande to Pecos. S. lohata was found 
commonly as a weed along irrigation ditches at Pecos and at Barstow. 
S. suhhastata was a common weed adjoining fields near Pecos. 
C. Trans-Pecos Plateau and Mountains below 4000 feet 
Area: Extends from the Great Plains on the east to New Mexico on 
the west and from the Rio Grande to New Mexico on the north. This 
area belongs to three climatic zones: the Lower Sonoran below 4,000 feet, 
the Upper vSonoran above 4,000 feet, and the Transition on the highest 
peaks of the Davis and Guadalupe mountains. Topography: This is an 
area of low mountains separated by plains and basins that have been formed 
mostly from the debris derived from the erosion of the mountains and by 
lava flows. Most of the mountains are broad and somewhat flat. Soil: 
In many arid and semi-arid localities "caliche" is a characteristic formation. 
"Caliche" is a deposit of lime formed by the evaporation of waters carrying 
calcium carbonate. This forms the "cap rock" of the high plains. Ele- 
vation: In the Rio Grande Valley near Boquillas the elevation is about 
I, 500 feet. The highest elevation is 8,690 feet, on El Capitan in the Guada- 
lupe Mountains near the New Mexican line. At Fort Davis the elevation is 
5,000 feet, at El Paso 3,762 feet. Rainfall: The annual mean for most of 
the region is from 9 to 20 inches; at Fort Davis it is 17.4 inches, at El Paso 
9.8 inches. Temperature: The annual mean temperature at El Paso is 
62.9°. Clear Days: The percentage of clear days at El Paso in 191 8 was 
56.4. Humidity: The mean annual evaporation for this region, according 
to Hill, is 70-90 inches. 
In the Rio Grande Valley, willows, cottonwoods, mesquite, and screw - 
bean {Strombocarpa puhescens) are important species. On dry plains and 
slopes, yuccas, agaves, numerous cacti, Dasylirion spp., Nolina spp., Fou- 
quiera splendens, Covillea tridentata, low mesquites, shrubby acacias, and 
mimosas are abundant. Open short-grass plains separate the mountains in 
the vicinity of Alpine and Marfa. On higher slopes, in the Upper Sonoran 
Zone, Pinus edulis, Juniperus spp., and Quercus spp. compose the chief 
elements of the vegetation. 
Abutilon incanum and A. parvulum were found rarely, A. wrightii 
frequently, on rocky slopes in this area. A. malacum was abundant on 
rocky hillsides and mountain sides along the Rio Grande from Boquillas 
to El Paso and in the vicinity of Balmorhea. Hibiscus denudatus var. 
involucellatus was frequent from Boquillas and Marathon throughout the 
Big Bend to El Paso on rocky slopes. H. coulteri was found in similar 
